Baxi Combi 80 Maxflue User guide

Baxi Combi 80 Maxflue
Gas Fired Wall Mounted Combination Boiler
Installation and
Servicing Instructions
Please leave these instructions with the user

2
Baxi UK Limited is one of the leading manufacturers
of domestic heating products in the UK.
Our first priority is to give a high quality service to our
customers. Quality is designed into every Baxi
product - products which fulfil the demands and needs
of customers, offering choice, efficiency and reliability.
To keep ahead of changing trends, we have made a
commitment to develop new ideas using the
latest technology - with the aim of continuing to make
the products that customers want to buy.
Everyone who works at Baxi has a commitment to
quality because we know that satisfied customers
mean continued success.
We hope you get a satisfactory service from Baxi. If
not, please let us know.
Natural Gas
Baxi Combi 80 Maxflue
G.C.No47 075 07
Baxi is a BS-EN ISO 9001
Accredited Company
The boiler meets the requirements of Statutory Instrument
“ The Boiler (Efficiency) Regulations 1993 No3083” and is
deemed to meet the requirements of Directive 92/42/EEC
on the energy efficiency requirements for new hot water
boilers fired with liquid or gaseous fuels:-
Type test for purpose of Regulation 5 certified by:
Notified Body 0051.
Product/Production certified by:
Notified Body 0051.
For GB/IE only.

3
1.0 Introduction 4
2.0 General Layout 5
3.0 Appliance Operation 6
4.0 Technical Data 7
5.0 Dimensions and Fixings 8
6.0 System Details 9
7.0 Site Requirements 12
8.0 Installation 18
9.0 Commissioning the Boiler 23
10.0 Completion 25
11.0 Servicing the Boiler 26
12.0 Changing Components 28
13.0 Illustrated Wiring Diagram 37
14.0 Fault Finding 38
15.0 Short Parts List 43
Section Page
Contents

Baxi UK Limited declare that no substances
harmful to health are contained in the
appliance or used during appliance
manufacture.
1.1 Description
1. The Baxi Combi 80 Maxflue is a fully automatic
gas fired wall mounted combination boiler. It is
room sealed and fan assisted, and will serve
central heating and mains fed domestic hot water.
2. The boiler is set to give a maximum output of
24.0 kW for hot water and central heating.
3. It is designed for use on Natural Gas (G20) and
can be converted to use Propane or Butane.
4. The boiler is suitable for use only on fully
pumped sealed heating systems. Priority is given
to domestic hot water.
5. The boiler data badge gives details of the
model, serial number and Gas Council number
and is situated on the control box. It is visible when
the case front panel is removed (Fig. 1).
6. The boiler is intended for use with an 80mm
diameter twin flue system. The system must be
installed in conjunction with a single roof terminal
or two separate flue and air terminals.
7. Separate terminals do not have to be on the
same wall but must not be on opposite walls of the
dwelling.
8. The separate terminals allow greater flexibility
when siting the boiler - see Sections 7.8 to 7.13 of
Site Requirements for full details of available flue
components, maximum lengths etc.
9. The boiler is intended to be installed in
residential / commercial / light industrial E.M.C.
environments on a governed meter supply only.
10. All systems must be thoroughly flushed
and treated with inhibitor (see section 6.2).
1.2 Installation
1. The appliance is suitable for installation only in
G.B. and I.E. and should be installed in
accordance with the rules in force. For Ireland
install in accordance with I.S.813 “INSTALLATION OF
GAS APPLIANCES”. The installation must be carried
out by a CORGI Registered Installer or other
competent person and be in accordance with the
relevant requirements of GAS SAFETY (Installation
and Use) REGULATIONS, the BUILDING REGULATIONS
(Scotland) (Consolidation), the LOCAL BUILDING
REGULATIONS, the CURRENT I.E.E. WIRING
REGULATIONS and the bye laws of the Local Water
Undertaking. Where no specific instructions are
given, reference should be made to the relevant
BRITISH STANDARD CODES OF PRACTICE.
1.3 Optional Extras
Various control accessories, LPG conversion kits
etc. are available as optional extras. These are
detailed in a separate publication.
1.0 Introduction
4
Data Badge
Fig. 1
Control Box
“Benchmark”Log Book
As part of the industry-wide “Benchmark”initiative all Baxi boilers now
include an Installation, Commissioning and Service Record Log Book.
Please read the Log Book carefully and complete all sections relevant to
the appliance and installation. These include sections on the type of
controls employed, flushing the system, burner operating pressure etc.
The details of the Log Book will be required in the event of any warranty
work. Also, there is a section to be completed at each subsequent regular
service visit. The Log Book must be left with the user.
Case Front Panel
NOTE: This appliance must be installed
in accordance with the manufacturer’s
instructions and the regulations in force.
Read the instructions fully before
installing or using the appliance.

2.0 General Layout
5
2.1 Layout
1. Air Pressure Switch
2. Expansion Vessel
3. Burner Manifold
4. Automatic Air Vent
5. DHW Plate Heat Exchanger
6. Circulation Pump
7. Drain Off Point
8. Pressure Relief Valve
9. Position For Optional Integral Timer
10. Central Heating System Pressure Gauge
11. PCB
12. Control Box
13. 3-Way Valve Assembly
14. Flame Sensing Electrode
15. Spark Electrode
16. Burner
17. Primary Heat Exchanger
18. Fan Assembly
19. On/Off/Reset Selector Switch
20. Central Heating Temperature Control
21. Hot Water Temperature Control
22. Flame Failure
23. Safety Thermostat
24. Fault on Fan or Flue
25. Fault on Pump or Low System Pressure
26. Fault on Hot Water Sensor
27. Fault on Central Heating Sensor
28. Power On
29. Hot Water Mode
30. Central Heating / Hot Water Mode
31. Burner On
When neons 22 to 27 are constantly illuminated,
they indicate the temperature of the central heating
water.
18
17
16
14
15
13
12 11
10 9
19 20 21 10 9
7
6
3
4
5
8
2
1
30°40°50°60°70°80°
2
1
0
4
3
bar
30°40°50°60°70°80°
22 23 24 25 26 27
28 29 30 31

3.0 Appliance Operation
6
NOTE: All delay timers mentioned in 3.1 and
3.2 are overridden by domestic hot water
demand.
3.1 Central Heating Mode (Fig. 2)
1. With a demand for heating, the pump circulates
water through the primary circuit. At a flow rate of
approximately 125 l/hr the central heating flow
switch operates, initiating the ignition sequence.
2. The main burner ignites at low rate, then the
gas valve controls the gas rate to maintain the
heating temperature measured by the thermostat
sensor.
3. When the flow temperature exceeds the setting
temperature, a 3 minute delay occurs before the
burner relights automatically (anti-cycling). The
pump continues to run during this period.
4. When the demand is satisfied the burner is
extinguished and the pump continues to run for a
period of 3 minutes (Pump Overrun).
3.2 Domestic Hot Water Mode (Fig. 3)
1. Priority is given to the domestic hot water
supply. A demand at a tap or shower will override
any central heating requirement.
2. The flow of water will operate the DHW flow
switch which causes the 3 way valve to change
position. This will allow the pump to circulate the
primary water through the DHW plate heat
exchanger.
3. The burner will light automatically and the
temperature of the domestic hot water is
controlled by the thermostat sensor.
4. When the domestic hot water demand ceases
the burner will extinguish and the diverter valve
will remain in the domestic hot water mode,
unless there is a demand for central heating.
IMPORTANT: When the selector switch is in
the ‘0’(Off) position the electrical supply to the
boiler is isolated. The boiler will not operate
and the integral timer (if fitted) will require
resetting once the selector switch is set to
either the DHW position or CH position.
3.3 Frost Protection Mode
1. The frost protection mode is integral to the
appliance and functions only with the selector
switch (see Section 2.1) in the domestic hot water
and central heating position. If the system
temperature falls below 5°C then the boiler will
fire on its minimum setting until a flow temperature
of 30°C is reached. Further protection can be
incorporated by using a system frost thermostat.
3.4 Pump Protection
1. With the selector switch (see Section 2.1) in
either the central heating or central heating and
hot water position the pump will automatically
operate for 1 minute in every 24 hours to prevent
sticking
1
2
4
5 6
7
8
9
10
11
1213141516
17
18
19
20
21
22
23
24
25
26
3
1 Primary Heat Exchanger
2 Burner
3 Ignition Electrode
4 Flame Sensing Electrode
5 Gas Valve
6Pump
7 Automatic Air Vent
8 Plate Heat Exchanger
9 Flow Sensor with Filter
10 Pressure Relief Valve
11 Boiler Drain Point
12 Heating Return
13 Cold Water Inlet On/Off Valve and Filter
14 Gas Inlet
15 Domestic Hot Water Outlet
16 Heating Flow
17 Pressure Gauge
18 Hydraulic Differential Pressure Sensor Microswitch
19 Automatic By-Pass
20 Hydraulic Differential Pressure Sensor
21 Diverter Valve Assembly
22 Domestic Hot Water Flow Priority Assembly
23 Domestic Hot Water Flow Priority Microswitch
24 Overheat Thermostat
25 Central Heating NTC Sensor
26 Expansion Vessel
27 Domestic Hot Water NTC Sensor
Key
Central Heating Circuit
Domestic Hot Water Circuit
Fig. 3
1
2
4
5 6
7
8
9
10
11
1213141516
17
18
19
20
21
22
23
24
25
26
3
Fig. 2
27
27

4.0 Technical Data
7
Flue Terminal Diameter 80mm
Dimensions Projection 80mm
Outercase Dimensions
Casing Height - 780mm
Overall Height Inc Flue
Elbow - 980mm
Casing Width - 450mm
Casing Depth - 345mm
Clearances
Both Sides 5 mm Min
Above Casing 200 mm Min
Below Casing 200 mm Min
Front 450 mm Min (For Servicing)
Front 5 mm Min (In Operation)
Weights kg
Packaged Boiler Carton 47.5
Packaged Flue Kit 2.5
Installation Lift Weight 39.5
Central Heating Primary Circuit
Pressures
bar
Safety Discharge 3
Max Operating 2.5
Min Operating 0.5
Recommend Operating 1-2
DHW Circuit bar
Pressures
Max Operating 8
Min Operating 0.2
Min Operating Pressure
at 9.8 l/min 0.9
Flow Rates l/min
DHW Flow Rate
@ 30o C Rise 13.7
DHW Flow Rate
@ 35o C Rise 9.8
Min Working
DHW Flow Rate 2.5
Pump
Available Head See graph below
Expansion Vessel - (For Central Heating
only. Integral with appliance)
bar
Min Pre-charge Pressure 0.5
litre
Max Capacity of
CH System 125
Primary Water Content
of Boiler (unpressurised) 1.0
Connections copper tails
Gas Supply - 22mm
Central Heating Flow - 22mm
Central Heating Return - 22mm
Cold Water Mains Inlet - 15mm
DHW Flow - 15mm
Pressure Relief Discharge - 15mm
Temperatures
C.H. Flow Temp (adjustable)
35°C to 85°C max (± 5°C)
D.H.W. Flow Temp (adjustable)
35°C to 65°C max (± 5°C)
dependent upon flow rate
Heat Input C/H & DHW (Gross)
kW 26.3 Max
Btu/h 89,739 Max
Heat Output Max Min
kW 24.0 9.3
Btu/h 81,891 31,730
Electrical Supply 230V~ 50Hz
(Appliance must be connected to an
earthed supply)
Power Consumption 170W
External Fuse Rating 3A
Internal Fuse Rating
Fuse 2A Fast Blow to BS 4265
Appliance Category CAT II 2H 3+
Max Gas Rate (Natural Gas)
(After 10 Mins)
m3/h 2.78
ft3/h 98.12
Inlet Pressure (Natural Gas)
mbar 20
in wg 8
Burner Injector (Natural Gas)
15 x 1.18mm Diameter
Burner Pressure (Natural Gas)
Max Rate Min Rate
mbar 10.6 ± 0.5 1.9 ± 0.2
in wg 4.24 ± 0.2 0.76 ± 0.2
0
200 400 600 800 1000 1200
0.5
1
1.5
2
2.5
3
3.5
4
Metre wg
l/h
Pump - Available Head
0
Appliance Type C12 C32 C52 NOxClass 3
This value is used in the UK Government’s Standard
Assessment Procedure (SAP) for energy rating of dwellings.
The test data from which it has been calculated have been
certified by 0051.
SEDBUK Declaration For Combi 80 Maxflue
The seasonal efficiency (SEDBUK) is 78.5 %
Electrical Protection
IPX5D
4.1 Combi 80 Maxflue
LPG Gases Propane - G31 and
Butane - G30
Burner Injector 15 x 0.69
Burner Pressure Max Rate Min Rate
Propane mbar 35.8 6.2
in wg 14.3 2.5
Butane mbar 28.0 4.7
in wg 11.2 1.9
Inlet Pressures Propane Butane
mbar 37 30
in wg 14.8 12

5.0 Dimensions and Fixings
8
Dimensions
A780mm
B345mm
C450mm
Domestic Hot
Water Outlet
(15mm)
Cold Water
Inlet
(15mm)
Heating
Return
(22mm)
Heating
Flow
(22mm)
Pressure Relief
Valve
(15mm)
Gas
Inlet
(22mm)
65 mm 65 mm 65 mm 65 mm 65 mm
Tap Rail
A
C
B

6.0 System Details
9
6.1 Information
1. The Baxi Combi 80 Maxflue Combination Boiler
is a ‘Water Bylaws Scheme - Approved Product’.
To comply with the Water Bylaws your attention is
drawn to the following installation requirements
and notes (IRN).
a) IRN 001 - See text of entry for installation
requirements and notes.
b) IRN 302 - Bylaw 14.
2. Reference to the WRC publications, ‘Water fittings
and materials directory’and ‘Water supply bylaws
guide’give full details of bylaws and the IRNs.
6.2 Central Heating Circuit
1. The appliance is suitable for fully pumped
SEALED SYSTEMS ONLY.
Treatment of Water Circulating Systems
•All recirculatory water systems will be subject to
corrosion unless an appropriate water treatment is
applied. This means that the efficiency of the
system will deteriorate as corrosion sludge
accumulates within the system, risking damage to
pump and valves, boiler noise and circulation
problems.
•For optimum performance after installation this
boiler and its associated central heating system
must be flushed in accordance with the guidelines
given in BS 7593 “Treatment of water in domestic
hot water central heating systems”.
•This must involve the use of a proprietary
cleanser, such as BetzDearborn Sentinel X300 or
X400, or Fernox Superfloc. Full instructions are
supplied with the products, but for immediate
information please contact BetzDearborn (0151
420 9563) or Fernox (01799 550 811) directly.
•For long term protection against corrosion and
scale, after flushing it is recommended that an
inhibitor such as BetzDearborn Sentinel X100, or
Fernox MB-1 or Copal is dosed in accordance with
the guidelines given in BS 7593.
Failure to flush and add inhibitor to the system
may invalidate the appliance warranty.
•It is important to check the inhibitor
concentration after installation, system modification
and at every service in accordance with the
manufacturer’s instructions. (Test kits are available
from inhibitor stockists.)
•For information or advice regarding any of the
above contact Baxi Technical Enquires.
6.3 Bypass
1. The boiler is fitted with an automatic integral
bypass.
6.4 System Control
1. The boiler is designed for use in a heating
system that incorporates external controls, i.e. a
minimum of a timer device.
2. Suitable timer kits are available as optional
extras.
3. For optimum operating conditions and maximum
economy the fitting of a programmable room
thermostat, such as the Baxi Combi Controller, is
recommended.

Stop
Valve
Double
Check
Valve
DHW
Mains
Inlet
CH
Return
Temporary
Hose
6.0 System Details
10
6.5 System Filling and Pressurising
1. A filling point connection on the central heating
return pipework must be provided to facilitate
initial filling and pressurising and also any
subsequent water loss replacement/refilling.
2. There are connection points on the mains cold
water inlet and central heating return isolating
taps (Fig. 4a) to which the optional filling loop kit
(Part No. 248221) can be assembled.
3. The filling method adopted must be in
accordance with the Water Supply (Water
Fittings) regulations and the Water Bylaws
(Scotland).
4. Your attention is drawn to: Paragraph 24 of
Schedule 2 Section 8 of the publication Water
Regulations Guide which gives recommendations
and guidance on approved methods for filling
sealed systems.
5. The sealed primary circuits may be filled or
replenished by means of a temporary connection
between the primary circuit and a supply pipe
provided the arrangement in accordance with
Diagram R24.2a of the Water Regulations Guide.
6. The temporary hose must be completely
removed at both ends after use.
6.6 Expansion Vessel
(Central Heating only)
1. The appliance expansion vessel is pre-charged
to 0.5 bar. Therefore, the minimum cold fill
pressure is 0.5 bar. The vessel is suitable for
correct operation for system capacities up to 125
litres. For greater system capacities an additional
expansion vessel must be fitted - refer to BS 7074
Pt 1.
6.7 Pressure Relief Valve (Fig. 5)
1. The pressure relief valve is set at 3 bar,
therefore all pipework, fittings, etc. should be
suitable for pressures in excess of 3 bar.
2. The pressure relief discharge pipe should be
not less than 15mm dia, run continuously
downward, and discharge outside the building,
preferably over a drain. It should be routed in
such a manner that no hazard occurs to
occupants or causes damage to wiring or
electrical components. The end of the pipe should
terminate facing down and towards the wall.
3. The discharge must not be above a window,
entrance or other public access. Consideration
must be given to the possibility that boiling
water/steam could discharge from the pipe.
Fig. 4
Fig. 5
Pressure Relief Valve
Discharge Pipe
Stop
Valve
Filling Loop
Fig. 4a